To realize a low carbon society and to secure energy, efficient use of fossil fuels such as coal and oil is effective. For example, when burning coal in an iron-making blast furnace and a coal-fired power generation, which are comparatively large emission sources of CO2, oxygen (pure oxygen) or air (oxygen-enriched air), the oxygen concentration of which is increased compared to that of the atmosphere (air) as is, is blown instead of the atmosphere. This allows coal to be subjected to high-calorie burning and, as a result, thermal efficiency is increased.
Patent Literature 1 describes a cryogenic separation method as a method of producing pure, oxygen used for high-calorie burning of fossil fuel as described above. In this method, after air has been cooled and liquefied, oxygen is fractionated from the air by utilizing the difference in boiling point between oxygen and nitrogen.
Among practically used methods of producing oxygen or oxygen-enriched air, the above-described cryogenic separation method can produce oxygen or the like at a lowest cost. However, nowadays, there is a demand for further reducing the cost of oxygen or oxygen-enriched air.
However, with the above-described cryogenic separation method, since air is cooled to a cryogenic temperature and liquefied, a theoretical limit of Carnot refrigerator efficiency cannot be exceeded in principle. Specifically, the theoretical value of energy efficiency in the cryogenic separation method is low: equal to or less than 34%. With the cryogenic separation method, energy efficiency equal to or higher than the above-described value cannot be obtained.
Thus, it is very difficult to produce oxygen or oxygen-enriched air so as to further reduce the unit cost of production.
Patent Literature 2 describes a device that produces oxygen-enriched air from room-temperature air (about 300 K).
This device removes part of nitrogen from air so as to produce oxygen-enriched air by utilizing the fact that, among the components of air, only oxygen is paramagnetic and other components are non-magnetic.
Specifically, as illustrated in FIG. 14, this device includes a cylindrical container 102 and a pair of magnets 104. Air flows in the container 102, which is formed of a non-magnetic material. The pair of magnets 104 form a magnetic field in the container 102 in a direction perpendicular to the air flow direction. The air flowing in the container 102 is supplied from one end portion 102a of the container 102. Two separator plates 106 are disposed at another end portion 102b of the container 102. These two separator plates 106 have leading ends in the magnetic field formed by the pair of magnets 104 and are disposed in a position perpendicular to the magnetic field and parallel to each other. Thus, two separator plates 106 divide a region on the other end side in the container 102 into three sections in a direction perpendicular to the magnetic field. A first passage tube 110 is connected to an outlet 108b. In the container 102, the outlet 108b is open at the end of a central channel 108 interposed between two separator plates 106. Second passage tubes 114 are connected to respective outlets 112b. In the container 102, the outlets 112b are open at the ends of respective side channels 112 positioned on both sides of the central channel 108 with the central channel 108 interposed therebetween.
In a device 100 having the above-described structure, air supplied from the one end portion 102a flows toward the other end portion 102b in the container 102. When the air enters the magnetic field formed by the pair of magnets 104, only oxygen in the air is magnetized. Thus, components of the air other than oxygen straightly advances toward the other end portion 102b in the container 102 without being affected by the magnetic field. In contrast, the magnetized oxygen advances in a path bent by the magnetic field formed by the pair of magnets 104. Referring to FIG. 14, the magnetized oxygen is bent rightward or leftward and enters the side channels 112. Thus, air containing an increased amount of oxygen (oxygen-enriched air) is exhausted to the second passage tubes 114. By collecting the exhausted air, a specified amount of oxygen-enriched air is obtained.
Production of oxygen-enriched air from room-temperature air (300 K) is simulated by using the above-described device 100 that utilizes the magnetic field. The difference in oxygen concentration between room-temperature air and the oxygen-enriched air produced from this room-temperature air is about 0.1%. Furthermore, in the above-described device 100, a very high magnetic field gradient of, for example, 100 T/m, needs to be formed in the air flow direction in the container 102. Thus, producing this device for actual and practical use is very difficult.